Miniature reverberation chamber system



y 30, 1961 M. RETTINGER ETAL 2,986,228

MINIATURE REVERBERATION CHAMBER SYSTEM 4 Sheets-Sheet 1 Filed May 8,1957 v rbkllllllllll r Pr||||ll|||| a I lll. IIIIIIII/ INVENTORS.MICHAEL RETTINGER a CARL u. SHIPMAN ATTORNEY 4 Sheets-Sheet 2 5 f f W WM. RETTINGER ETAL MINIATURE REVERBERATION CHAMBER SYSTEM May 30, 1961Filed May 8, 1957 l r v:

INVENTORS. MICHAEL RETTINOER G N. SHIPIAN ATTORNEY M. RETTINGER ET AL2,986,228 MINIATURE REVERBERATION CHAMBER SYSTEM May 30, 1961 Filed May8, 1957 4 Sheets-Sheet 3 C I X4 I -25 Q t I: I g f 5 a 2 ,2! Q Z6 Q 30 Ill i 7 q M INVENTORS. MICHAEL RETTINGER a 4 CARL u. smpmm BY ATTORNE 7.

y 1961 M. RETTINGER ETAL 2,986,228

MINIATURE REVERBERATION CHAMBER SYSTEM Filed May 8, 1957 4 Sheets-Sheet4 INVENTORS.

MICHAEL RETTINOER l CARL N. SHIPMAN ATTORNEY United States PatentMINIATURE REVERBERATION CHAMBER SYSTEM Michael Rettinger, Encino, andCarl N. Shipman, Jr.,

Rivera, Calif., assignors to Radio Corporaticn of America, a corporationof Delaware Filed May 8, 1957, Ser. No. 657,940

6 Claims. (Cl. 181-.5)

This invention relates to sound recording and reproducing systems, andparticularly to that portion thereof whereby the characteristics ofsound waves are modified before being recorded or reproduced.

Patent No. 2,431,962, of December 2, 1947, discloses and claims areverberation chamber system in which the various wall sections of thechambers have no parallel surfaces, the chambers having a loudspeakertherein for generating sound waves and a microphone therein fordetecting the waves. In this manner, various reverberationcharacteristics are obtainable, particularly by the use of a partitionhaving a door between the diflerent size chambers. The chamber system ofthis patent, however, is of considerable size, thus requiring a largeamount of space and expensive construction.

The present invention is directed to a reverberation chamber which willprovide the same reverberation time as the patented chamber but whichmay be reduced in size from twenty-five to thirty times that of thepatented chamber. Such a small chamber, therefore, is more economical toconstruct and may be placed in any normal size room wherever it isdesired to modify sound waves being recorded or reproduced.

The principal feature which permits the large reduction in size of thechamber is the use of a heavy gas within the chamber plus the use ofmetal panels for the walls of the chamber. That is, for a gas having adensity of approximately nine times that of air, a 27-fold reduction inchamber volume is possible. Several gases are operative, such astungsten fluoride, vaporized mercury, and several types of Freon.

The reverberation chamber is enclosed within an outer chamber to preventnoise from being transmitted into the chamber as well as to prevent thereverberated sound from being transmitted into the room in which theentire unit is located. Bracing is provided between the opposite wallsof the reverberation chamber to reduce excessive vibration of the walls.Furthermore, a 45-degree baffle is positioned along one corner of thechamber opposite the loudspeaker generating the sound waves to preventwave parallelism between the speaker and opposite wall to avoid theproduction of standing waves.

The principal object of the invention, therefore, is to facilitate theobtaining of reverberated sound.

Another object of the invention is to provide an improved system forobtaining reverberated sound.

A further object of the invention is to provide an improvedreverberation system of miniature size and low cost.

A better understanding of this invention may be had from the followingdetailed description when read in connection with the accompanyingdrawings, in which:

Fig. 1 is a perspective view of a reverberation chamber embodying theinvention;

Fig. 2 is a cross-sectional view of the reverberation chamber shown inFig. 1 and its outer enclosure taken on a plane corresponding to theline 2-2 of Fig. 1 and viewed in the direction of the appended arrows;

Fig. 3 is a cross-sectional view of the reverberation chamber shown inFig. 2;

Fig. 4 is a cross-sectional view of the loudspeaker unit taken along theline 4-4 of Fig. 2;

Fig. 5 is a detailed view of the microphone and its mounting taken alongthe line 5-5 of Fig. 2; and

Fig. 6 is a detail drawing of the microphone mounting taken along theline 6-6 of Fig. 5.

Referring, now, to the drawings in which the same reference numeralsindicate the same elements, a rectangular casing 5 may be constructed ofdifferent types of rigid material, one such material being .109" steelwhich may or may not be treated externally with a mastic 6 such as thatused to underseal automobiles. The chambers may be of different sizes,one satisfactory size being 24" x 38" x 60 /2" which has a volume of 32cubic feet. Because the chamber is built of steel, the boundaryabsorptivity is very low.

To avoid excessive panel vibration, the chamber is stiffened internallyby 1" thick steel pipe braces. For instance, between the walls 8 and 9are pipes 10, and between the walls 12 and 13 are pipes 14, and betweenthe upper wall 16 and bottom wall 17 are pipes 18. Although a certainnumber of stiiiening members are shown for the purpose of illustration,more or fewer stifiening members may be used if desired, depending uponthe amount of stiffening required. Angle iron may also be used asstifiening braces.

In addition to preventing excessive panel vibration, the pipes also actas sound difiusers within the enclosure. Furthermore, at the lowerleft-hand corner of Fig. 2 is shown a panel deflector 20 atapproximately 45 degrees to the adjoining walls, this deflector aidingin deflecting the sound between the walls 8 and 9 as mentioned above.

To introduce sound into the chamber 5, a loudspeaker shown generally at21 is mounted in an opening in the wall 16 as shown in detail in Fig. 4.The loudspeaker may be of any general type, having a casing 23, a magnet24, a voice coil 25, and a diaphragm 26. The casing 23 is fastened tothe wall 16 by machine bolts 28 through a flange 30, the casing 23 andwall 16 being separated by a rubber gasket 29. The outer rim of theloudspeaker diaphragm 26 is mounted on a ring 31 on which a support 32for the magnet 24 and conductors 33 is also mounted. The seal is suchthat a vacuum may be created within the chamber 5 to permit the highdensity gas to be subsequently introduced in the chamber.

Also attached to wall 16 is a microphone support which includes a collar35 supporting three rods 36, at the lower ends of which is mounted amicrophone 37 within a collar 38, to which are attached springs 39having their other ends connected to the rods 36. The microphone may beof any standard type, its output circuit being connected over conductors41 to external apparatus. The mounting of the microphone is also suchthat a vacuum may be created within the chamber 5, the mountingconsisting of a rubber gasket 42 interposed between a sealing ring 43and the wall 16 and being held in position by machine bolts 44. Thus,sound is introduced into the chamber 5 by the loudspeakers 21 anddetected by the microphone 37.

As shown in Figs. 2 and 3, the chamber 5 is enclosed within a secondchamber 46 to insure a low noise level within the steel chamber 5 and toprevent the sound waves within the inner chamber from being transmittedexternally. The enclosing chamber 46 is made of plywood 47 and is linedwith approximately /2" of an acoustic material 48, such as acoustictile. The chamber casing 5 rests upon vibration isolators 50 and is heldin position by wedge blocks 51. The chamber 5 is exhausted of airthrough an opening 53, after which a gas, such as a selected type ofFreon, is introduced therein to provide a, the desired reverberationtime. After the heavy gas is in-the chamber 5, the opening 53 is closedin any suitable manner, such as by a plug 54. The reverberation time ofa chamber having the above-mentioned dimensions and filled with Freongas is of the order of approximately four seconds, which is-the same asa chamber twenty-seven times larger in volume and filled with air.

Two preferred typesof Freon gas are known as Du Pontdichlorodifluoromethane (CCL F type 12 and Du Pontmonochloropentafluoroethane (CClF CF type 115.

We claim:

1. A miniature sizereverberation chamber system'capable of providing thesame reverberation times as those of larger reverberation chamberscomprising a firstenclosure, a sound-absorbing material along theintegral surface of the walls ofsaid'enclosure, a second enclosureWithin said first enclosure in spaced relation to said sound absorbingmaterial, a plurality of braces extending between-the opposite wallsofsaid second enclosure for preventing excessive vibration thereof,means enclosed by said first enclosure and disposed-in the space betweensaid second enclosure and said sound absorbing material for projectingsound waves within said second enclosure, means Within said secondenclosure for detecting sound waves within said second enclosure, and agas Within said second'enclosure, said gas-having a density greater thanair.

2. A miniature size reverberation-chamber system in accordance withclaim 1 in which said means for-projecting sound waves within saidsecond enclosure is carried by said second enclosure and extendstherefrom outwardly into'said space.

3. A miniature size reverberation chamber system in accordance withclaim 1 in which the density of said gas is approximately nine timesthat of air to provide a reverberation time comparable to anenclosureapproximately twenty-seven times as large in volume assaidsecond enclosure.

4. A miniature size reverberation chamber system-in accordance withclaim 1 in which said gas is a type-of Freon.

S. A miniature size reverberation chamber system capable of providingthe same reverberation times as those of larger reverberation chamberscomprising a first enclosure a sound absorbing material along-theinternal surface of the walls of said enclosure, a second enclosurewithin said first enclosure and-air spaced therefrom, a plurality ofbraces extending between the opposite walls of said second enclosure forpreventing excessive vibration thereof, means enclosed by said firstenclosure for projecting sound waves within said second enclosure, meanswithin said second enclosure for detecting sound waves within saidsecond enclosure, a gas within said enclosure having a density greaterthan air, and a sound wave deflecting baflle positioned within saidsecond enclosure at approximately 45 to the wall opposite said means forprojecting sound waves within said second enclosure.

6. A miniature size, reverberation chamber system capable of providingthe same reverberation times as those of larger reverberation chamberscomprising a first enclosure, a sound absorbing material along theinternal surface of the walls of said enclosure, a second enclosurewithin saidfirst enclosure in spaced relation to said sound absorbingmaterial, means enclosed by said first enclosure'and disposed in thespace between said second enclosure and said sound absorbing materialfor projectingsound waves within said second enclosure, means withinsaidsecond enclosure for detecting sound waves within said secondenclosure, and a gas within said second enclosure, said gas having adensity greater than air.

"References Cited in thefile of this patent UNITED STATES PATENTS 2,06

OTHER 5R EF ERENCES Knudsen: Absorption ,of'Sound in Air, Oxygen, etc.,Journal of Acoustical Society of America, October 1933, vol. V, pages1124121.

Beranek: Acoustic Measurements, published by John Wiley & Sons, Inc.,New York, 1949, page 866.

"Hansen: Simple Echo, Box, Radio-Electronics Magazine, July 1952pagesSl, 52.

